Method and apparatus for 2-d spatially resolved optical emission and absorption spectroscopy

ABSTRACT

A multi-point detection method and system for analyzing a composition within an examination area. The system simultaneously acquires multi-dimensional distributions (e.g., two- or three-dimensional distributions) of plasma optical emissions at at least two wavelengths. Such diagnostics are useful for real-time spatially-resolved measurements of plasma electron temperature distributions and/or chemical species concentrations within a plasma processing chamber ( 50 ). Generally, the system analyzes/diagnoses the measurement of line-of-sight light emission or absorption in the plasma.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention is directed to a method and apparatus forresolving optical emissions and absorptions, and more particularly to amethod and apparatus for resolving optical emissions and absorptions inat least two dimensions.

[0003] 2. Discussion of the Background

[0004] Recently, the use of optical diagnostics in plasma processingtools has seen a significant increase. Optical diagnostics provide thebenefits of real-time signal acquisition along with being inherentlynon-intrusive. Known systems using optical diagnostics, such as opticalemission spectroscopy, acquire signals from only a single line of sightin space at a time, typically via an optical fiber feed. At one end,light emitted from the plasma passes through a small aperture (or iris)located outside an optical vacuum window and it is focussed onto one endof the optical fiber via a focusing lens. The opposite end of theoptical fiber is generally optically connected to the input of aspectrometer, wherein the light spectrum may be dispersed via a gratingand the incremental wavelength spectrum recorded using a photo-detector.In such a system, acquiring a signal from another line of sight in spacerequires repositioning of the optical system, meaning that themeasurement at the next point in space is not done at the same time asfor the previous line(s) of sight.

[0005] Other known optical systems use multiple fixed optical fiberfeeds. The use of multiple feeds allows the estimation of the variation,at the same instant of time, of the measured property within some regionof the plasma, but such systems do not support full multi-dimensionaldistributions of measured plasma properties since they suffer from the“one optical fiber channel per measurement line of sight” limitation.Moreover, such systems also suffer from the fact that the opticalemission or absorption they intend to measure is, in actuality, theintegrated light emitted or absorbed along the line of sight which fallswithin the field of view of the optical apparatus.

[0006] One method and device for detecting the end point of a plasmaprocess is disclosed in U.S. Pat. No. 5,980,767 (hereinafter “the '767patent”), assigned to the assignee of the present invention. FIG. 1 ofthe '767 patent is reproduced as FIG. 1 of the present application. Inthat figure, a single detector 22 is used to analyze the condition ofthe plasma.

SUMMARY OF THE INVENTION

[0007] It is an object of the present invention to provide a multi-pointdetection method and system for analyzing a composition within anexamination area. This object, and other advantages of the presentinvention, are addressed by a system that simultaneously acquiresmulti-dimensional distributions (e.g., two- or three-dimensionaldistributions) of plasma optical emissions at at least two wavelengths.Such diagnostics are useful for real-time spatially-resolvedmeasurements of plasma electron temperature distributions and/orchemical species concentrations within a plasma processing chamber.Generally, the system analyzes/diagnoses the measurement ofline-of-sight light emission or absorption in the plasma.

BRIEF DESCRIPTION OF THE DRAWINGS

[0008] A more complete appreciation of the invention and many of theattendant advantages thereof will be readily obtained as the samebecomes better understood by reference to the following detaileddescription when considered in connection with the accompanyingdrawings, wherein:

[0009]FIG. 1 is a schematic illustration of an optical end pointdetector system as described in a known system;

[0010]FIG. 2 is a schematic illustration of a multi-detector systemaccording to the present invention; and

[0011]FIG. 3 is a schematic illustration of a computer for analyzing thesampled emission and/or absorption data according to the presentinvention.

DESCRIPTION OF THE PREFERRED EMBODIMENT

[0012] Referring now to the drawings, wherein like reference numeralsdesignate identical or corresponding parts throughout the several views,FIG. 2 is a schematic illustration of one embodiment of the presentinvention used to collect information about the processing conditions ofa wafer 45 within a chamber 50. At least two detectors 52 are locatedcircumferentially outside the processing chamber 50 such that lightpasses through corresponding viewports. Each detector 52 has a viewingangle Θ (e.g. the angle of the “fan of light rays” seen by thedetector). Light emitted from the chamber 50 is passed through afocusing lens 54 and an optical system 55 such that the incoming lightrays are projected onto a beam splitter 60 by way of reflectors 57(e.g., mirrors). The beam splitters 60 separate the light rays into twobeams, each of which is passed through an optical filter 62 of adequatebandpass, set at the wavelength whose intensity needs to be monitored.Many different devices can be used as optical filters, e.g. coloredglass and thin-film coated filters, etc. The two filtered beams are thensent onto a line-CCD device array 64, which is used to measure theirlight intensities. The optical system is designed in such a way thateach pixel readout on the line-CCD corresponds to the light intensity atthe desired wavelength of an incoming light ray on the detector, one ofmany rays in the “ray fan”. Acquisition of light intensities on all CCDarrays, for all wavelengths and in all detectors can be madesimultaneous with appropriate trigger/electronic shutter circuitry.Those intensities are passed to a data acquisition system 95, whichpasses the acquired data to a computer 100. (In an alternate embodiment,data can be provided to the computer 100 directly from the CCDs 64.) Ingeneral, with a minimum of two detectors, and once a set of intensityprofiles has been read from all CCDs, a numerical procedure called“tomographic inversion” (also known as “Abel inversion”) can be used torecover the full two-dimensional distributions of light emission, at thetwo wavelengths, in a region of the plasma where the “ray fans” of theset of detectors intersect. The application of tomographic inversion (orAbel inversion) to such a set of data is discussed in detail in GaborHerman's monographs “Image Reconstruction from Projections: TheFundamentals of Computerized Tomography” and “Image Reconstruction fromProjections: Implementation and Applications”, and they are hereinincorporated by reference in their entirety. These two-dimensionaldistributions can then be used to obtain plasma properties of interest.The measurements are simultaneous on all detectors, and thus a “snapshotin time” is obtained of the plasma property distribution of interest.With the use of appropriate (e.g. fast, electronically shuttering) CCDs,suitable triggering/shutter control electronics, and large buffermemories for measurement storage, one can acquire plasma propertydistributions in rapid succession, which allows the study oftime-evolving phenomena in the plasma, such as chemical speciesconcentrations.

[0013] In an alternate embodiment, the system provides multi-wavelengthacquisition without a speed/repetition rate penalty. Such an embodimentsplits the beam into plural channels with filters and line-CCDdetectors. Although acquisition can be done on two wavelengths,additional wavelengths can also be monitored. For example, by adding “n”additional splitters and “n” additional filters (where n>=1) and byusing another CCD (or another part or parts of a multi-frequency CCD),an (n+2)-wavelength detector can be provided. The same software thathandled the first two wavelengths would then take care of the additionaln wavelengths.

[0014] Such a system can be extended to three dimensions by addingadditional planes of detection (e.g., above or below the plane formed bythe detector array fan shown in FIG. 2). Using three dimensions, thechanges in the plasma can be analyzed across volumes of the plasma.

[0015] Referring now to the drawings, wherein like reference numeralsdesignate identical or corresponding parts throughout the several views,FIG. 3 is a schematic illustration of a computer system for measuringtwo-dimensional distributions of light emissions. A computer 100implements the method of the present invention, wherein the computerhousing 102 houses a motherboard 104 which contains a CPU 106, memory108 (e.g., DRAM, ROM, EPROM, EEPROM, SRAM, SDRAM, and Flash RAM), andother optional special purpose logic devices (e.g., ASICs) orconfigurable logic devices (e.g., GAL and reprogramable FPGA). Thecomputer 100 also includes plural input devices, (e.g., a keyboard 122and mouse 124), and a display card 110 for controlling monitor 120. Inaddition, the computer system 100 further includes a floppy disk drive114; other removable media devices (e.g., compact disc 119, tape, andremovable magneto-optical media (not shown)); and a hard disk 112, orother fixed, high density media drives, connected using an appropriatedevice bus (e.g., a SCSI bus, an Enhanced IDE bus, or a Ultra DMA bus).Also connected to the same device bus or another device bus, thecomputer 100 may additionally include a compact disc reader 118, acompact disc reader/writer unit (not shown) or a compact disc jukebox(not shown). Although compact disc 119 is shown in a CD caddy, thecompact disc 119 can be inserted directly into CD-ROM drives which donot require caddies. In addition, a printer (not shown) also providesprinted listings of two-dimensional distributions of light emissions.

[0016] As stated above, the system includes at least one computerreadable medium. Examples of computer readable media are compact discs119, hard disks 112, floppy disks, tape, magneto-optical disks, PROMs(EPROM, EEPROM, Flash EPROM), DRAM, SRAM, SDRAM, etc. Stored on any oneor on a combination of computer readable media, the present inventionincludes software for controlling both the hardware of the computer 100and for enabling the computer 100 to interact with a human user. Suchsoftware may include, but is not limited to, device drivers, operatingsystems and user applications, such as development tools. Such computerreadable media further includes the computer program product of thepresent invention for calculating two-dimensional distributions of lightemissions. The computer code devices of the present invention can be anyinterpreted or executable code mechanism, including but not limited toscripts, interpreters, dynamic link libraries, Java classes, andcomplete executable programs.

[0017] Obviously, numerous modifications and variations of the presentinvention are possible in light of the above teachings. It is thereforeto be understood that, within the scope of the appended claims, theinvention may be practiced otherwise than as specifically describedherein.

1. In a plasma processing chamber for processing substrates, wherein theprocessing chamber includes plural optical viewports, the improvementcomprising: a first optical system for receiving a first series of lightbeams in a first direction; a first detector for receiving the firstseries of light beams from the first optical system; a second opticalsystem for receiving a second series of light beams in a seconddirection; a second detector for receiving the second series of lightbeams from the optical system; and a calculator for calculatingtwo-dimensional distributions of light emissions from substantiallysimultaneous outputs of the first and second detectors, wherein at leasta portion of the first and second series of light beams pass across acommon area within the plasma processing chamber.
 2. The improvement asclaimed in claim 1, wherein the first and second directions aresubstantially perpendicular.
 3. The improvement as claimed in claim 1,wherein the first and second optical systems comprise at least one beamsplitter.
 4. The improvement as claimed in claim 1, wherein the firstand second detectors comprise multi-frequency detectors.
 5. Theimprovement as claimed in claim 1, wherein the first and seconddetectors comprise CCDs.
 6. The improvement as claimed in claim 1,wherein the first and second optical systems comprise at least onefilter interposed between the plasma processing chamber-and the firstand second detectors.
 7. The improvement as claimed in claim 1, whereinthe substrate comprises a wafer.
 8. The improvement as claimed in claim1, wherein the calculator for calculating two-dimensional distributionsof light emissions comprises a computer.